To subvert means to turn from below. We need a new word, which means to turn from above. The primary threat to the democratic state and its functions comes not from mob rule or leftwing insurrection, but from the very rich and the corporations they run.

Over the last few years I have been trying better to understand how the demands of big business and the very rich are projected into policymaking, and I have come to see the neoliberal thinktanks as central to this process. These are the groups which claim to champion the free market but whose proposals often look like a prescription for corporate power.

Soon after it was founded (in 1977), the institute approached "all the top companies". About 20 of them responded by sending cheques. Its most enthusiastic supporter was the coup plotter James Goldsmith, one of the most unscrupulous asset strippers of that time. Before making one of his donations, Pirie writes, "he listened carefully as we outlined the project, his eyes twinkling at the audacity and scale of it. Then he had his secretary hand us a cheque for £12,000 as we left".

From the beginning, senior journalists on the Telegraph, the Times and the Daily Mail volunteered their services. Every Saturday, in a wine bar called the Cork and Bottle, Margaret Thatcher's researchers and leader writers and columnists from the Times and Telegraph met staff from the Adam Smith Institute and the Institute of Economic Affairs. Over lunch, they "planned strategy for the week ahead". These meetings would "co-ordinate our activities to make us more effective collectively". The journalists would then turn the institute's proposals into leader columns while the researchers buttonholed shadow ministers.

Soon, Pirie says, the Mail began running a supportive article on the leader page every time the Adam Smith Institute published something. The paper's then editor, David English, oversaw these articles himself, and helped the institute to refine its arguments.

As Pirie's history progresses, all references to funding cease. Apart from tickets donated by British Airways, no sponsors are named beyond the early 1980s. While the institute claims to campaign on behalf of "the open society", it is secretive and unaccountable. Today it flatly refuses to saywho funds it.

Pirie describes how his group devised and refined many of the headline policies implemented by Thatcher and John Major. He claims (and produces plenty of evidence to support it) either full or partial credit for the privatisation of the railways and other industries, for the contracting-out of public services to private companies, for the poll tax, the sale of council houses, the internal markets in education and health, the establishment of private prisons, GP fundholding and commissioning and, later, for George Osborne's tax policies.

Pirie also wrote the manifesto of the neoliberal wing of Thatcher's government, No Turning Back. Officially, the authors of the document – which was published by the party – were MPs such as Michael Forsyth, Peter Lilley and Michael Portillo. "Nowhere was there any mention of, or connection to, myself or the Adam Smith Institute. They paid me my £1,000 and we were all happy." Pirie's report became the central charter of the doctrine we now call Thatcherism, whose praetorian guard called itself the No Turning Back group.

Today's parliamentary equivalent is the Free Enterprise Group. Five of its members have just published a similar manifesto, Britannia Unchained. Echoing the narrative developed by the neoliberal thinktanks, they blame welfare payments and the mindset of the poor for the UK's appalling record on social mobility, suggest the need for much greater cuts and hint that the answer is the comprehensive demolition of the welfare system. It is subtler than No Turning Back. There are fewer of the direct demands and terrifying plans: these movements have learned something in the past 30 years.

It is hard to think how their manifesto could have been better tailored to corporate interests. As if to reinforce the point, the cover carries a quote from Sir Terry Leahy, until recently the chief executive of Tesco: "The path is clear. We have to be brave enough to take it."

I see these people as rightwing vanguardists, mobilising first to break and then to capture a political system that is meant to belong to all of us. Like Marxist insurrectionaries, they often talk about smashing things, about "creative destruction", about the breaking of chains and the slipping of leashes. But in this case they appear to be trying to free the rich from the constraints of democracy. And at the moment they are winning.